1. Field of the Invention
The invention relates to a feedthrough for a storage device, in particular a battery feedthrough, for a battery such as a lithium-ion battery, a lithium ion accumulator or a capacitor, as well as to the use of sealing glass to feed a metallic conductor through and into the housing of a storage device.
2. Description of the Related Art
Lithium-ion batteries and accumulators are provided for a multitude of applications, for example for portable electronic devices, cell phones, power tools and electric vehicles. Lithium-ion batteries, in particular for applications in the automobile industry, generally feature a multitude of individual battery cells that are connected in-series. The in-series connected battery cells are combined into so-called battery packs; several battery packs then into a battery module which is also referred to as lithium-ion battery. Each individual battery cell comprises electrodes which are led out of a housing of the battery cell. These batteries can replace conventional energy sources, for example lead-acid batteries, nickel-cadmium batteries or nickel-metal hydride batteries.
For batteries, in particular lithium-ion batteries and accumulators, light metals or light metal alloys such as aluminum alloys are often used as the housing material for the battery or as electric conductor, in particular for certain applications, especially in the automobile industry, but also for aircraft. This use in the automobile field raises a multitude of problems such as corrosion-resistance, stability in accidents or vibration resistance. An additional problem is the hermetic impermeability of the battery, in particular of the lithium-ion battery over a long period of time. The impermeability may, for example, be compromised by leakage in the area of the electrodes of the battery or respectively the electrode feed-through of the battery, by a battery short-circuit or temperature changes leading to a reduced life span of the battery. An additional problem with battery feedthroughs is the instability with respect to the aggressive battery electrolytes, especially with respect to non-aqueous electrolytes as are used for example, in lithium-ion accumulators.
In order to ensure better stability in accidents, a housing for a lithium-ion battery is suggested, for example, in DE 101 05 877 A1, whereby the housing includes a metal jacket which is open on both sides and which is being sealed. The power connection is insulated by a synthetic material. A disadvantage of synthetic material insulations is the limited temperature resistance and the uncertain impermeability over the service life.
Moreover it is known to use so-called sealing glasses or, respectively, solder glasses for metallic-electric feedthroughs that—in addition to electric insulation of the conductors—must also have a hermetic sealing function. A variety of possible design forms are described for this in the current state of the art.
U.S. Pat. No. 6,037,539 A and U.S. Pat. No. 5,965,469 A disclose a high frequency feedthrough (HF-feedthrough) wherein a ferrous or non-ferrous conductor in an aluminum-phosphate glass or alkali-aluminum-phosphate glass composition is fed through a housing component comprising aluminum. However, no battery feedthroughs are described.
WO 03/061034 A1 (EP 1 464 089 A1) moreover relates to an arrangement having a glass to metal seal for use in conjunction with a lithium-ion electrolyte, comprising a metallic body comprising a chemically stable metal, a chemically stable metallic electrically conductive pin and a glass material arranged between the metallic body and the pin, and with electric insulation of both, whereby the glass material presents a phosphate-rich composition, such as ALSG-32 glass.
DE 10 2011 012 430 A1 and WO 2012/110244 A1 describe a feedthrough having a base body, in particular in the form of preferably a disk-shaped metal part, whereby the base body has at least one opening through which at least one essentially pin-shaped conductor, embedded in a glass or glass ceramic material is guided, wherein the base body comprises a material having a low melting point, in particular a light metal, preferably aluminum or AlSiC and whereby the glass or glass ceramic material is selected so that the sealing temperature of the glass or glass ceramic material comprising the material having the low melting temperature is below the melting temperature of the base body having the low melting temperature. The glass or glass ceramic material is selected for example from the glass families of silicate-titanate, sulpho-phosphate, telluride, boride, vanadate, fluoride, phosphate or silicate.
WO 2012/110242 A1 and DE 10 2009 030 951 respectively describe a feedthrough, in particular for a lithium-ion battery whereby essentially pin-shaped conductor, embedded in a glass or glass ceramic material is guided through an opening in a base body. A glass or glass ceramic material having high phosphate content is preferably selected.
Glasses for direct sealing with metals and alloys having high thermal expansion have become known from DE 1049063 B, said glasses having a content of 4 to 30 weight-% TiO2, whereby the glasses known from DE 1049063 B have an obligatory 2 to 8 weight-% SrO. SrO is advantageously used to reduce the melting temperatures and the glass transition temperature. Higher SrO content can moreover bring about an increase of the thermal coefficient of expansion. Nevertheless, SrO is an expensive raw material and using higher contents of SrO can have negative properties in regard to chemical stability of the glasses, in particular in regard to resistance to acids.
Glass systems are therefore frequently described in the current state of the art as suitable solder glasses for the cited application examples that have a high phosphate proportion, for example a phosphate proportion of >30 weight-%. These phosphate containing solder glasses are characterized, for example, in that they have a similarly high CTE (coefficient of thermal expansion) as aluminum alloys, that is in the range of 15 to 25×10−6 1/K. Based on their composition, aluminum alloys have CTE's, for example, between 20 to 26×10−5 1/K; this is however determined essentially by the main alloy components, for example Si, Mg, Cu, Mn, and Zn.
These glass systems often have at the same time a relatively low transformation temperature (Tg) that is below the melting point or melting interval of aluminum alloys. This renders them suitable, among other factors, for the designated application. The transformation temperatures (Tg) of the solder glasses are hereby between 300 and 450° C.
Phosphate containing glasses are used as solder glasses in the current state of the art since they are very resistant to anhydrous battery electrolytes. The electrolyte consists, for example, substantially of a mixture of LiPF6 and organic carbonates. A test to determine the resistance of a solder glass against an electrolyte—meaning, how much solder glass material is being dissolved by the electrolyte—is the so-called leaching. Typical leaching values are specified, for example, in WO 2012/110242 A1 in table 1 on page 19.
The production of glasses having such high phosphor content is however associated with considerable difficulties. The phosphor and/or phosphate contents can, for example, attach to the crucible or vat material during the melting process due to which the molten glass could—on the one hand—be contaminated and, on the other hand, the life span of the glass melting device could be considerably shortened. The phosphor and/or phosphate contents could furthermore easily evaporate from the molten glass, making expensive air filtration systems necessary, so that these components do not get into the environment. This increases the production costs considerably. Moreover, the filtration residue must be disposed of in an environmentally friendly manner.
Based on the described disadvantages of the current state of the art, what is needed in the art is a feedthrough of the type previously specified that can be produced with a sealing glass and which can be produced at a reduced manufacturing cost and in a more environmentally friendly manner.